Fire alarm systems equipped with circuit monitoring devices

ABSTRACT

A fire alarm system including a plurality of fire alarms arranged in groups. Alarm-simulating conditions are produced in each fire alarm by an electric test signal, the response of each fire alarm being sent to an evaluation device at a central signal station through a circuit coupling the fire alarms together. Each alarm generates an oscillation in normal condition which is suppressed in the alarm state.

United States Patent Walthard et a1. 1451 July 18, 1972 s41 FIRE ALARMSYSTEMS EQUIPPED [56] References Clted WITH CIRCUIT MONITORING UNITEDSTATES PATENTS DEVICES 2,667,630 1/1954 Jorgcnsen ..340/410 72Inventors; Beat w m Andras s hd n 2,917,731 12/1959 Rodgers ....340/2l4Max Kuhn, all of Stafa, Switzerland 3,064,245 11/1962 Lindberg....340/410 3,134,970 5/1964 Kelly ....340/4l0 [73] Assgnee- Manned,swtzerlan 3,192,506 6/1965 Henn ....340/410 [22] Filed: Oct. 5, 19703,235,858 2/1966 Mader ..340/214 [211 App! 78u7 Pn'mary Examiner-ThomasB. Habeclcer Related us. Application om AlwmeyWemerW-K1eeman [62] :1Ser. No. 636,174, May 4, 1967, Pat. No. [57] ABSTRACT A fire alarmsystem including a plurality of fire alarms ar- [30] Foreign ApplicationPriority Data ranged in groups. Alarm-simulating conditions are producedin each fire alarm by an electric test signal, the response of May 9,1966 Swrtzerland ..6703/66 each fire alarm being sent to an evaluationdevice at a Central 52 us. c1. ..340/410, 340/228 R Sign a drum s 1 1Int. Cl. G08b 29/00 [58] Field of Search ..340/4l0, 214 h alarmgenerates an il i i normal condition which is suppressed in the alarmstate.

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Patented July 18, 1972 X TEM r5177 EVAL. MEANS Eixls RFRNC ION/Z/IT/ONCHAMBER 22 42 25 MEASUR/Aki 23 mzwznrmu CHAMBER G9 INVENTOR 1 Am REA!Kuhn 3m Mash BY S h-Judah: & HR)

The instant application is a divisional application of our commonlyassigned, co-pending U.S. application, Ser. No. 636,174, filed May 4,1967 and entitled FIRE ALARM SYSTEM HAVING A DIODE COUPLED CHECKING CIR-CUIT", now U.S. Pat. No. 3,564,524.

BACKGROUND OF THE INVENTION The present invention relates to an improvedfire alarm system comprising a central signal station to which electricfire alarms are connected in groups, wherein the number of conductorsbetween the central signal station and the fire alarms is independent ofthe number of fire alarms. Furthermore, the inventive fire alarm systemadditionally includes an apparatus for producing electrical test signalsby means of which alarm-simulating conditions are produced at the firealarms which, in turn, bring about an electrical change in condition atan intact fire alarm, and further, the inventive system includes anapparatus for evaluating such changes and conditions.

In fire alarm installations, there generally exists the requirement ofchecking the operational reliability of the individual fire alarms atregular intervals. To this end, and in accordance with a workablemethod, alarm-simulating conditions are manually delivered to theindividual fire alarms one after the other or in series. The response ofthe relevant alarm is controlled at its locality or at the centralstation. However, this technique is above all, extremely time-consumingand uneconomical, if the installation consists of a larger number offire alarms, for instance, one hundred fire alarms or more. In suchcase, a regular manual monitoring at shorter time intervals can nolonger be considered for practical reasons.

It is for these reasons that methods have been developed in which it ispossible to achieve from the central station alarmsimulating conditionsat the fire alarms through use of special electronic means, and to checkthe response conditions of all fire alarms at the central station. Thedifficulty with such method, above all, resides in the reliabledetermination of whether all fire alarms of a group have actuallyresponded.

In a known system, a separate conductor is lead from each fire alarmback to the central station. During the checking operation, a signalappears at such conductor which is characteristic of the responsecondition of the relevant fire alarm. This system has the drawback thatit requires extensive additional installations, which becomes ofparticular importance if such a monitoring device should be subsequentlyinstalled in an already existing fire alarm system.

Consequently, it is desirable to provide a monitoring device in whichthe number of conductors leading from the central station to the firealarms is independent of the number of con- 7 nected fire alarms. In aknown arrangement of this type, all of the fire alarms aresimultaneously caused to respond from the location of the centralstation. Further, by means of a current measuring device at the centralstation which is provided at one of both current delivery conductors ofthe fire alarm, the response of all fire alarms is monitored, wherebythere is checked the coincidence of the total current with somepredetermined reference value. Apart from the great current consumptionwhich has an adverse effect upon the choice and dimensioning of theconductors, the network devices, the emergency power groups, etc., thisarrangement is limited to groups having relatively few fire alarms.Because of the diversity of the electrical characteristics of thestructural elements or components in the fire alarms as well as becauseof the limited measuring accuracy during comparison of the total currentwith the reference value based upon an analogous measurement, thistechnique is unreliable with a larger number of fire alarms andoftentimes results in false alarms.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of thepresent invention to provide an improved monitoring device for a firealarm system of the previously mentioned type in which it is possible toreliably check or monitor an optional large number of fire alarms pergroup.

It is another object of the present invention to provide a monitoringsystem which may be installed in existing fire alarm systems.

It is a further object of the present invention to provide a monitoringsystem which requires low additional power.

It is an additional object of the present invention to provide amonitoring system which makes use of digital techniques.

Generally speaking, the present invention is characterized by thefeatures that the fire alarms of a group are coupled with one another bymeans of a logic circuit and that the logic circuit, during the checkingoperation, then delivers a signal to the evaluation device when all firealarms of a group have responded or at least one fire alarm has notresponded.

A number of different embodiment of the invention as well as furtherinventive features will be described in greater detail hereinafter inconjunction with the figures of the drawing. In this regard, it will beappreciated that while the exemplary fire alarm installations depictedherein are in each instance equipped with ionization fire alarms, itwould be equally well possible to also employ optical flame detectingalarms, smoke detecting alarms or temperature detecting alarms.

BRIEF DESCRIPTION OF THE DRAWING The invention will be betterunderstood, and objects other than those set forth above, will becomeapparent, when consideration is given to the following detaileddescription thereof. Such description makes reference to the annexeddrawing wherein:

FIG. 1 illustrates a circuit diag'ramof a first embodiment of theinvention in which the individual fire alarms have associated therewithdiode means for coupling the individual fire alarms to one another; and

FIG. 2 is a circuit diagram of an exemplary embodiment of the inventionin which the individual fire alarms have associated therewithoscillation generators.

DESCRIPTION OF THE PREFERREDEMBODIMENTS Describing now the drawing, inFIG. 1, there are depicted two fire alarms 39 and 40 of identicalconstruction. These fire alarms 39 and 40 are connected parallel to oneanother via the supply conductors or leads 35 and 36 as well as beingconnected via an additional signal conductor 29 with a central station41. As already remarked, these fire: alarms 39 and 40 are of identicalconstruction and preferably consist of two ionization chambers 21 and22, the air content of which can be rendered completely or'partiallyconductive through an appropriate radioactive preparation as is known inthe art. Furthermore, these fire alarms 39 and 40 each incorporate aswitch element 23 which, in this case, is a field-effect transistor. Theionization chamber 21 operates as a measuring chamber, whereas theionization chamber 22 is used as a reference chamber. Chamber 22 can bereplaced by a highohm resistor or an equivalent high-ohm element.Likewise, in lieu of a field-effect transistor 23 it is possible to useother semi-conductor devices or a different switch element with high-ohminput resistance or impedance, for instance a coldcathode tube.

The drain or anode of the field-effect transistor 23 is connected via aresistor 25 with the negative :supply conductor 35, the source orcathode via the tap of a potentiometer 24 with the positive supplyconductor 36. Furthermore, at the drain or anode of the field-effecttransistor 23 there is connected the gate of a controlled rectifier 26,the cathode of which is coupled with the negative supply cathode 35 andthe anode of which, on the one hand, is connected via a resistor 44 tothe negative supply conductor 35 and, on the other hand, via a resistor45 with the positive supply conductor 36. The anode of the controlledrectifier 26 is furthermore connected with the signal conductor 29through the series circuit or connection incorporating the indicatinglamp 31 and the Zener diode 28. A resistor 34 is connected in parallelwith the indicating lamp 31. This resistor 34 maintains the connectionbetween the controlled rectifier 26 and the Zener diode 28 duringbreakdown of the indicating lamp 31.

The potential at the tap of the potentionmeter 24 is adjusted in such amanner that the field-effect transistor 23 and thereby the controlledrectifier 26 block in the normal condition. The signal conductor 29 isconnected at the central station 41 via a contact of the switch 43 and aresistor 30 with the positive pole of the voltage source designated byreference numeral 100. The zener voltage of the diode 28 is selected insuch a manner that when the rectifier 26 is blocked, in which case itsanode has a potential determined by the voltage divider 44, 45, thisdiode 28 likewise blocks. The signal conductor 29 is then withoutcurrent and the voltage at points 200 equals the voltage of source 100.

Now if combustion gas enter the measuring chamber 21, then thefield-effect transistor 23 and the controlled rectifier 26 change theirswitched condition. More precisely, the potential at the anode of thecontrolled rectifier 26 practically drops to that of the supplyconductor 35 (ground), so that the voltage across the diode 28 nowexceeds the Zener voltage and the diode begins to conduct. At thecentral station 41 the voltage at point 200 or the contact of the switch43 drops from the voltage of source 100 value to a new valueapproximately corresponding to the Zener voltage of the diode 28. In sodoing, the resistor 30 is selected in such a manner that the currentflowing through the indicating lamp 3] initially does not cause such tolight up or indicate. By closing a switch 33 arranged parallel theresistor 30, the indicating lamp 31, in the case of the alarm, can becaused to ignite from the central station, whereby the fire alarmreceives a receipt or acknowledgement of the proper reception of thealarm signal at the central station.

The Zener diodes 28 of the individual fire alarms enable an alarm signalof the one or other fire alarm arrive via the common conductor at thecentral station without having any effect upon the remaining firealarms. In accordance with the invention, the OR-gate is coupled orswitched during the checking operation in such a manner that a signalonly appears at the central station if at least one fire alarm has notresponded. This can be realized in that, the conductor 29 is supplied bya voltage source 300 by means of the switch 43. The value of voltagesource 300 is smaller than the Zener voltage of the diodes 28. Since thevoltage of source 300 is smaller than voltage of source 100, the Zenerdiodes 28 are poled in the forward direction via the resistor 45 and theindicating lamps 31 and a current flows through the signal conductor.The alarmsimulating conditions are produced through opening for a shorttime the switch 37 to thus introduce a voltage reducing Zener diode 38in the supply conductor 36 which initially causes the capacitor 42 topartially discharge. Upon closing of the switch 37, a momentaryover-voltage is produced between the gate and cathode of thefield-effect transistor 23. The alarm-simulating conditions thus bringabout a response of the field-effect transistor 23 and thereby thecontrolled rectifier 26. Then, as a practical matter, the voltage ofsource 300 appears across the Zener diodes 28 of the intact fire alarms,which voltage by definition is smaller than the Zener voltage. If all ofthe fire alarms of a group have properly responded then the conductor 29is without current. On the other hand, a signal appearing at theconductor 29 means that one or more fire alarms have not responded.

The return of the fire alarm can likewise take place by means of thesignal conductor 29. To this end, the switch 43 is thrown or applied fora short time to a negative voltage source 400.

Naturally, it is also possible to apply numerous modifications to thecircuit of FIG. 1. Thus, for instance, it is possible to employconventional diodes instead of Zener diodes, whereby the measures whichmust be undertaken in such case will be apparent to those skilled in theart.

FIG. 2 depicts a circuit diagram of an embodiment of the invention whichis essentially based upon the same principles as the circuit diagram ofFIG. 1. in this circuit arrangement the individual fire alarms areconnected with one another into a logical circuit and an additionalsignal conductor is dispensed with.

By referring to FIG. 2 in greater detail it will be recognized that theindividual fire alarms 50 embody a measuring ionization chamber 52 and areference ionization chamber 54, the common connection point of which iscoupled with the starter electrode of a cold-cathode tube 56. The anodeof the coldcathode tube 56 is coupled via a resistor 58 with the supplyconductor 60 and the cathode is directly connected with the supplyconductor 62. Furthermore, between both of the conductors 62 and 60 aseries connection of a capacitor 64 and a resistor 66 is disposed. Atthe common juncture point or point of connection of the capacitor 64 andthe resistor 66 one electrode of the measuring ionization chamber 52 isconnected. The diode 68 is connected in parallel with the resistor 66.Finally, the anode of the cold-cathode tube 56 is connected via aresistor 70 with the connection point of a series connection of afurther capacitor 72 and a glow-discharge tube 74 disposed between thesupply conductors 60 and 62. Glowdischarge tube 74, capacitor 72 andresistors 58 and 70 form an impulse transmitter. A current flows throughthe glowdischarge tube 74 which charges the capacitor 72 for such lengthof time until the voltage is dropped via the glowdischarge tube 74 tothe extinguishing voltage, whereafter the capacitor 72 discharges viathe resistors 58 and 70. As a result, the voltage across theglow-discharge tube 74 again increases until it reaches the ignitionvoltage, and a new cycle is initiated. The individual current surges canbe registered at the secondary winding of a transformer 76 provided inthe supply conductor 62 at the central station 78.

If combustion gases enter the measuring ionization chamber 52, then thecold-cathode tube 56 ignites because of an increase of the starterpotential and draws a current through the resistor 58. In the event thatoperating voltage of the coldcathode tube 56 is larger than the ignitionvoltage of the glowdischarge tube 74 then the oscillations of theassociated impulse transmitter 74, 70, 72 stop. The current surge duringignition of the cold-cathode tube 56 can be employed in known manner fortriggering a relay 80 or another alarm-transmitting device.

The checking operation is initiated by dropping the supply voltage 500for a short period of time. In so doing, the capacitor 64 dischargesduring the reduction in voltage across the diode 68 to the new supplyvoltage. Now, if the supply voltage 500 is instanteously increased againto the old value, then the diode 68 once again blocks and the capacitor64 slowly charges via the high-ohm resistor 66. In so doing, however,the potential at the starter of the cold-cathode tube 56 initially is atan increased value determined by the capacitor 64 and the seriesconnection incorporating the ionization chambers 52-54 and the resistor58. The value of this potential is set in such a manner that thecold-cathode tube ignites. The sawtooth oscillations stop in the intactfire alarms, so that a signal only appears at the secondary winding ofthe transformer 76 which at the same time forms the input of anevaluation circuit or sensing device 19 when one or more fire alarmshave not responded.

After completion of the checking operation, the supply voltage 500 isdropped slightly below the operating voltage of the tube 56 andthereafter slowly again increased to the full value. In each case, thechecking operation is repeated at appropriate time-intervals.

While there is shown and described present preferred embodiments of theinvention, it is to be distinctly understood that the invention is notlimited thereto but may be otherwise variously embodied and practicedwithin the scope of the following claims. ACCORDINGLY,

What is claimed is: l. A fire alarm system comprising: a plurality offire alarms connected in parallel together in at least one group; acentral signal station; conductor means connecting said central signalstation with said plurality of fire alarms, the number of saidconductors being independent of the number of said fire alarms of eachgroup; means for generating an electric test signal during an alarmchecking operation; said fire alarms including means responsive to saidelectric test signal to cause each of said fire alarms which are in afunctionally ready state for detecting a fire condition to respond thesame as if an actual fire alarm condition were present; electricalcircuit means for said plurality of fire alarms for producing noalarm-checking response signals when all fire alarms of a group haveresponded to said electric test signal and producing an alarm-checkingresponse signal when at least one fire alarm of a group has notresponded to said electric test signal; and means for sensing at leastone of said respective response signals. 2. A fire alarm systemcomprising: a plurality of fire alarms connected in parallel together inat least one group; a central signal station; conductor means connectingsaid central signal station with said plurality of fire alarms, thenumber of said conductors being independent of the number of said firealarms of each group; means for generating an electric test signalduring an alarm checking operation; said fire alarms including meansresponsive to said electric test signal to cause each of said firealarms which are in a functionally ready state for detecting a firecondition to respond the same as if an actual fire alarm condition werepresent; 7 an electrical circuit means for said plurality of fire alarmsfor producing no alarm-checking response signals when all fire alarms ofa group have responded to said electric test signal and producing analarm-checking response signal when at least one fire alarm of a grouphas not responded to said electric test signal, each fire alarm includesan oscillator means, the oscillations of which are suppressed when eachsaid fire condition; and

means for sensing at least one of said respective response signals.

3. A fire alarm system as claimed in claim 2, wherein said conductormeans comprises two power supply conductors connected to each firealarm, said oscillator means of each fire alarm being connected togetherby one of said power supply conductors, a transformer having a primarywinding and a secondary winding electrically connected with saidelectrical circuit means, said primary winding being connected to saidone of said power supply conductors, and said secondary windingproviding the input of said means for sensing said response signals.

4. A fire alarm system as claimed :in claim 3, wherein said oscillatormeans comprises a saw-tooth generator.

5. A fire alarm system as claimed in claim 4, wherein said two powersupply conductors comprise a positive conductor and a negativeconductor.

6. A fire alarm system as claimed in claim 5, wherein said saw-toothgenerator includes a glow-discharge tube having an anode and a cathode,said cathode being connected to said negative conductor; a capacitor anda resistance means connected in arallel with said capacitor, oneterminal of said capacitor eing connected with said positive conductor,the other terminal of said capacitor being connected to said anode ofsaid glow-discharge tube.

7. A fire alarm system as claimed in claim 6, wherein said resistancemeans comprises a first and a second resistor connected in series; eachsaid fire alarm further comprising a cold-cathode tube having an anode,a cathode and a starter electrode, said anode electrode being connectedto the junction point of said first and second resistors, said cathodeelectrode being connected to said negative conductor; a third resistor;each of said fire alarms comprising a measuring ionization chamber and areference ionization chamber connected in series between said junctionpoint of said first and second resistors, and said third resistor; saidthird resistor being connected to said negative conductor; and meansconnecting said starter electrode of said cold-cathode tube to thejunction point between the measuring ionization chamber and thereference ionization chamber.

8. A fire alarm system as claimed in claim 7,each of said fire alarmsfurther including a second capacitor connected to said positiveconductor at one terminal thereof and connected to said third resistorat the other terminal thereof; a diode connected in parallel with saidthird resistor; and wherein said electric test signal comprises areduction in potential of said positive conductor.

alarm is in its fire alarm

1. A fire alarm system comprising: a plurality of fire alarms connected in parallel together in at least one group; a central signal station; conductor means connecting said central signal station with said plurality of fire alarms, the number of said conductors being independent of the number of said fire alarms of each group; means for generating an electric test signal during an alarm checking operation; said fire alarms including means responsive to said electric test signal to cause each of said fire alarms which are in a functionally ready state for detecting a fire condition to respond the same as if an actual fire alarm condition were present; electrical circuit means for said plurality of fire alarms for producing no alarm-checking response signals when all fire alarms of a group have responded to said electric test signal and producing an alarm-checking response signal when at least one fire alarm of a group has not responded to said electric test signal; and means for sensing at least one of said respective response signals.
 2. A fire alarm system comprising: a plurality of fire alarms connected in parallel together in at least one group; a central signal station; conductor means connecting said central signal station with said plurality of fire alarms, the number of said conductors being independent of the number of said fire alarms of each group; means for generating an electric test signal during an alarm checking operation; said fire alarms including means responsive to said electric test signal to cause each of said fire alarms which are in a functionally ready state for detecting a fire condition to respond the same as if an actual fire alarm condition were present; an electrical circuit means for said plurality of fire alarms for producing no alarm-checking response signals when all fire alarms of a group have responded to said electric test signal and producing an alarm-checking response signal when at least one fire alarm of a group has not responded to said electric test signal, each fire alarm includes an oscillator means, the oscillations of which are suppressed when each said fire alarm is in its fire alarm condition; and means for sensing at least one of said respective response signals.
 3. A fire alarm system as claimed in claim 2, wherein said conductor means comprises two power supply conductors coNnected to each fire alarm, said oscillator means of each fire alarm being connected together by one of said power supply conductors, a transformer having a primary winding and a secondary winding electrically connected with said electrical circuit means, said primary winding being connected to said one of said power supply conductors, and said secondary winding providing the input of said means for sensing said response signals.
 4. A fire alarm system as claimed in claim 3, wherein said oscillator means comprises a saw-tooth generator.
 5. A fire alarm system as claimed in claim 4, wherein said two power supply conductors comprise a positive conductor and a negative conductor.
 6. A fire alarm system as claimed in claim 5, wherein said saw-tooth generator includes a glow-discharge tube having an anode and a cathode, said cathode being connected to said negative conductor; a capacitor and a resistance means connected in parallel with said capacitor, one terminal of said capacitor being connected with said positive conductor, the other terminal of said capacitor being connected to said anode of said glow-discharge tube.
 7. A fire alarm system as claimed in claim 6, wherein said resistance means comprises a first and a second resistor connected in series; each said fire alarm further comprising a cold-cathode tube having an anode, a cathode and a starter electrode, said anode electrode being connected to the junction point of said first and second resistors, said cathode electrode being connected to said negative conductor; a third resistor; each of said fire alarms comprising a measuring ionization chamber and a reference ionization chamber connected in series between said junction point of said first and second resistors, and said third resistor; said third resistor being connected to said negative conductor; and means connecting said starter electrode of said cold-cathode tube to the junction point between the measuring ionization chamber and the reference ionization chamber.
 8. A fire alarm system as claimed in claim 7,each of said fire alarms further including a second capacitor connected to said positive conductor at one terminal thereof and connected to said third resistor at the other terminal thereof; a diode connected in parallel with said third resistor; and wherein said electric test signal comprises a reduction in potential of said positive conductor. 